Separation of selected components from hydrocarbon mixtures



Jan. 27, 1959 c. G.

SEPARATION OF SELECTED COMPONENTS FROM GERHOLD HYDROCARBON MIXTURES 2 Sheets-Sheet 1 Filed Aug. 17, 1953 3 2 Quas 3.0 m m SQ mu: 33m

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United States. Patent SEPARATION OF SELECTED COMPONENTS FROM HYDROCARBON MIXTURES Clarence George Gerholtl, Riverside, Ill., assignor to Universal Oil Products Company, Des Piaiues, 111., a corporation of Delaware Application August 17, 1953, Serial No. 374,467

6 Claims. (Cl. 260-676) This invention relates to an improved method of fractionally separating desired components from a mixture containing components boiling lower and higher than said desired components, and more particularly to the recovery of substantially pure overhead light gas such as hydrogen or methane and the like, or alternately to the recovery of light side-cuts of normally gaseous hydrocarbon components, as well as a-desired gasoline fraction, such as may be produced in a cracking or reforming unit, of either the thermal or catalytic type.

Briefly, it is a feature of this improved operation to make a preliminary separation of the mixture into a gaseous fraction and a liquid fraction within a receivingchamber and to pass the fractions separately to spaced points in an elongated fractionating column, with the gaseous fraction being introduced at a point below the top thereof, while the liquid fraction is introduced to a lower point. The desired side-cut fraction, or fractions, may be obtained from the column at a proper level between the points of introduction ofthe gas and liquid fraction.

In one embodiment the present invention relates to a method for fractionally separating and recovering a de-' sired component from a mixture of components having different boiling points comprising, separating said mixture into a gaseous fraction and a liquid fraction, said gaseous fraction containing a major proportion of components boiling below said desired component and said liquid fraction containing a major proportion of components boiling above said desired component, introducing the lower boiling fraction to a fractionating column at an intermediate point in the height of the column, simultaneously introducing the higher boiling fraction to said column at a lower point in the height thereof, withdrawing a liquid stream from the column below said lower point, removing a fraction from the column between the points of introducing the low and high boiling fractions and discharging a light fraction from the upper portion of the column.

In another embodiment the present invention'relates to a method for fractionally separating and recovering a desired component from a mixture containing'lower boiling and higher boiling components comprising, separating said mixture into a gaseous fraction and a liquid fraction, said gaseous fraction containing a major pro portion of components boiling below said desired component and said liquid fraction containing a major proportion of components boiling above said component, introducing the separated lower boiling fraction to a fractionating column at an intermediate point in the height of the column, simultaneously introducing the separated higher boiling fraction to said column at a lower point in the height thereof, contacting the gaseous fraction with a lean absorption oil in the upper portion of the column, passing the resultant enriched absorption oil downwardly in the column below said intermediate point and in this portion of the column removing dissolved gases from said liquid fraction and the absorption oil, withdrawing a liquid stream from the column below said lower point, removing a fraction from the column between the points of introducing the low and high boiling fractions and discharging a light gaseous fraction from the upper portion of the column.

The light side-cut fraction may be withdrawn as liquid or as vapor streams and subjected to cooling and condensation atcon'trolled conditions so that the resulting liquids provide fractions or mixtures, lower boiling than the stabilized fraction being withdrawn from a lower part of the fractionator. On the other hand, where it is desired to recover a particular overhead gaseous stream, the lower boiling side-cut fractions may be withdrawn as vapors Without subjecting them to condensation orreturnto the column.

Where light side-cut fractions are being recovered asdesired liquid components, in a preferred operation, the: uncondensed component of the vaporous side-cut streams are returned to the column with a portion of each stream which is not passed through the cooler and condenser, so that the combined stream is subjected to absorption in the upper portion of the combined stream whereby portions of the desired fractions which have not been removed will alternately return to the point of withdrawal for subsequent removal.

nately propane and butane, as a side-cut fraction for use as'L. P. G. (liquid petroleum gases), which have a high ly as liquids from the column and the liquid will contain the desired component, however, it is preferred to remove a gaseous side-cut and subject this gaseous side-cut to cooling and condensation to recover the desired liquid fraction. liquid a portion may be recycled back to the column.

As has been noted, it also is a feature of the present improved operation to effect the production of a dry gas stream fro-m the top of the column and very little con-- densable hydrocarbons. Such an operation may be of value with respect to certain catalytic reforming operations wherein hydrogen is utilized in the reforming operation and is passed to the fractionating section with the liquid-gas stream. An enhanced concentration of hydrogen within the dry gas stream is desirable to effect an easier recovery of the hydrogen for reuse in the catalytic reforming step.

In the preferred embodiment, therefore, a mixture con taining components with different boiling points is first separated into a'liquid fraction and a gaseous fraction and theseparation is made so that said liquid fraction a major proportion of components boiling below the dcsiredcornponentl This may readily be accomplished in a flash separator in which the pressure and temperature are soc'ontrolled as to give the desired separation. For example, a liquid-gas stream composed of hydrogen; methane, ethane, propane, butanes, pentanes, hexanes and heavier or higher'boiling hydrocarbons may be introduced into a separator and the pressure maintained at about 650 pounds per square inch and a temperature of about F. At these conditions the gaseous fraction will contain the major proportion of components boiling lower than propane and the liquid fraction will contain proportion (over 50%) of the hydrogen, methane and For example, in a reforming operation to provide a desired gasoline fraction, or alter-' When the side-cut is removed directly as a ethane while the liquid fraction contains the major proportion of the butanes, hexanes and heavier or higher boiling hydrocarbons. The propane is present in both fractions and the major proportion of propane may be present in either fraction. When it is desired that the propane side-cut be relatively free of light components, it is preferred that the major proportion of propane be present in the liquid, and similarly, when it is desired that the propane side-cut be almost completely free of heavier components, it is preferred that the major proportion of propane be present in the gas.

The component that is removed as a side-cut may be one particular hydrocarbon or it may be a mixture of hydrocarbons. In the above example only one compound was desired in the side-cut, however, by regulating the first'separation and fractionation the component may be a propane-butane mixture in which case the gaseous fraction would contain the major proportion of the components boiling lower than propane and the liquid fraction would contain the components boiling higher than butane.

As hereinbefore set forth, the lower boiling or gaseous fraction is introduced to a fractionating column at an intermediate point in the height of the column and simultaneously the higher boiling or liquid fraction is introduced to the column at a lower point in the height thereof. The fractions need not be introduced into the column in the state that they are removed from the fractionator, that is the lower boiling fraction may be partially condensed or completely condensed and introduced to the fractionator and the higher boiling fraction may likewise be partially or completely vaporized and introduced to the fractionator. The lower boiling fraction, regardless of whether it is in the liquid or gaseous state, must be introduced to the fractionator at a higher point than the higher boiling fraction. It is preferred, however, to introduce the light fraction in the gaseous state and the heavy fraction in the liquid state.

According to the invention, therefore, there is a primary separation and an introduction of a light fraction and a heavy fraction to a fractionating column. The desired component, which may be one or a mixture of compounds, is removed at a point between the points of introduction. In a preferred operation a gaseous side-cut is removed, partially condensed and the uncondensed portion returned to the column at a point above the withdrawal level. Using the method of this invention a component that is substantially uncontaminated by lighter or heavier components is removed as a side-cut from the fractionator. This is entirely different from conventional side-cuts which have very substantial amounts of lighter and heavier components present therein.

The present invention may best be described and explained in conjunction with the accompanying drawings which show an elevation view of preferred forms of the apparatus, incorporating features for carrying out the desired improved process. Figure 1 denotes a flow diagram of the process using a simple fractionator while Figure 2 represents a specific embodiment using an improved combination absorption-stabilization unit for the fractionating column.

Referring now to Figure 1, a stream comprising a mixture of lower boiling and higher boiling hydrocarbons such as, for example, gasoline distillates and lower boiling hydrocarbons and gases from a cracking or reforming unit, is discharged through line 1 and control valve 2 to a receiving chamber or separator 3, wherein the stream may be separated into liquid and gas phases. Propane is the desired component and the separation is made in receiver 3 such that components lighter than propane are predominately in the gaseous phase and components heavier than propane are predominately in the liquid phase. In accordance with the present invention, the liquid and gas phases are separately introduced into fractionating column 4. The gaseous stream is transferred from the receiver 3 through line 5, having control valve 6, to the column 4 at a point about one-third way down, while the liquid stream from the lower end of receiver 3 is passed through line 7, having control valve 8, to a lower point in the height of the column.

The spacing between the points of introducing the gaseous and liquid phases through the respective lines 5 and 7 will vary in accordance with the side-cut fraction to be withdrawn from the column 4 and with the corresponding amount of fractionation required to withdraw the side-cut. Column 4 contains a plurality of contacting means such as bubble trays, perforated plates, packing, or the like, as indicated in the present drawing by the plurality of horizontal broken lines 9, each contacting means being suitable to effect a countercurrent contact between ascending vapors and gases and descending liquid streams, as desired in a rectifying column.

The'light fraction of the charge, entering through line 5, passes upwardly from the point of introduction and in the upper section it is brought into contact with a reflux which enters the column through line 10. A relatively dry gas stream is withdrawn from the upper end of column 4 through line 11, passes through cooler 12 and into receiver 13 wherein the resulting liquid and vapor phases are separated. The vapor phase is withdrawn through line 14 containing control valve 15. The liquid phase is withdrawn through line 16 and some of it is returned to the column as reflux in line 10 containing control valve 17 and any excess liquid is withdrawn by way of line 18 containing control valve 19". In Figure 1, a single side-cut of a normally gaseous hydrocarbon fraction, such as propane, is indicated as being withdrawn from the column 4, while a gasoline fraction is withdrawn fro-m the lower portion of the column 4. For the propane side-cut a vapor phase is withdrawn from the column 4 at a point below the entrance of the lighter fraction through line 5 and above the point of entry of the heavier fraction through line 7, and at a location suitable to provide a propane side-cut of the desired characteristics. The vapor stream is withdrawn through line 19, with valve 26, therein adjusted such that a major portion of the stream is passed through line 21 having valve 22 and enters thecooler 23 to undergo partial condensation. The cooler and partially condensed ream from cooler 23 in turn passes by way of line 24 to' a receiver 25 wherein the resulting liquid and vapor phases are separated. By a proper location of the withdrawal line 19, a relatively pure fraction, in this case, propane, may be condensed within the receiver 25 and withdrawn from the lower end thereof through line 26 having valve 27. As hereinbefore mentioned, a propane fraction may be desired in certain localities as an L. P. G. gas, where demand may provide a high value for that fraction.

The uncondensed gaseous fraction from the receiver 25 is passed by way of line 28 having control valve 29 to a point where it combines with the portion of withdrawn vapor stream through line 19 and the mixture subsequently returned to the column 4 at a point above the withdrawal location. Thus the portion of the vapor not passed through the partial condensing equipment may join with the uncondensed components from the receiver 25 and return to the column where the vapors pass upwardly and the desired fraction or fractions not removed ultimately return to the point of withdrawal at line 1) where they may be removed. A line 30 having control valve 31 is indicated as connecting with line 28 and provides means for withdrawing a portion of the vapor stream from the system where such may be desired.

In the lower portion of column 4 the heavier fraction entering through line 7, passes downwardly through the lower contacting decks wherein they are freed of a substantial portion of the dissolved gases by contact with relatively hot ascending vapors and gases from the lower portion of the column 4. In the embodiment illustrated, therev is shown reboiler 32, connecting by means of line 33 having valve 34 and return line 35, such that sufficientheat may be supplied to the liquid fraction to insure the. withdrawal of a fraction relatively free of propane. The bottoms from column 4 are withdrawn through line 36 having control valve 38 and passed through cooler 37 and exits through line 39. The valve 38 is preferably controlled automatically by a level controller within the lower portion of column 4.

Figure 2 illustrates a specific embodiment of the invention and is different from Figure 1 chiefly in that the conventional fractionating, column 4 of Figure l is replaced, by a combined column, having an upper portion operating as an absorption zone 40, an intermediate zone as a rectification and stabilizing section 42, and a lower portion as a stripping section 43.

Referring now to Figure 2 the liquid-gas mixture is brought into a receiver or separator and introduced into fractionating column 4 in a similar manner to that shown in Figure 1. Numbers 1'-9' of Figure 2 correspond to numbers 1-9 of Figure 1. In accordance with the present invention the light fraction and heavy fraction are separately introduced into a combined column 4, having an upper portion 40 operating as an absorption zone, an intermediate zone 42 as a rectification and stabilizing section, and a lower portion 43 as a stripping section.

The light fraction components of the charge, entering through line 5', pass upwardly from the point of introduction and through the upper absorption zone or section 40 wherein they are brought into countercurrent contact with a lean absorption oil which is supplied at the upper end of the column through line 41, being obtained from the lower end of the column as will be hereinafter described. The absorption operation is carried out so that substantially all of the normally liquid components are recovered and at least a portion of the heavier normally gaseous fractions are absorbed by the oil. For example, where side-cut fractions of propane and butane are desired, then the absorption should be operated to eifect substantial absorption of the propane and butane fractions in order that they be carried downwardly into the fractionating section within the 'upper portion of zone 42, permitting only a relatively dry gas stream to pass from the upper end of the column 4" through line 11 having control valve 15'. The valve 15 is preferably a pressure controlling valve suitable to maintain a given desired pressure within the column 4. The valve may be hand controlled, but in a desirable automatic operation of the unit the valve is controlled by a pressure controlling means connecting with an intermediate portion of the column, such as with the lower portion of the stabilizing section 42 in order that a desired substantially constant pressure be maintained within that portion of the column where, for example, a desired gasoline fraction is being withdrawn.

The enriched absorber oil from the lower end of the absorption section 40, descends into the fractionation section in the upper portion of the rectifying section 42 and is countercurrently contacted by ascending vapors and gases from the lower section of the column. In Figure 2, a single side-cut stream of a normally gaseous hydrocarbon fraction, such as propane, is indicated as being withdrawn from the column 4, while a gasoline fraction is withdrawn from the lower portion of the rectification and stabilizing section as the principal desired component. For the propane side-cut the system is described by numbers 1931' which correspond to numbers 19-31 of Figure 1. i

In the lower portion of the rectifying-stabilizing zone 42, the enriched absorber oil, with unremoved normally gaseous fractions, together with the heavier fraction of the charge stream entering through line 7, passes downwardly through the lower contacting decks of zone 42 wherein they are freed of a substantial portion of the dissolved gases by contact with relatively hot ascending vapors and gases from the lower portion of the stabilizing section and the stripping section 43. In the embodiment shown, a collecting tray 44 is provided between the stabilizing section 42 and the stripping section 43 such that a pool of stabilized gasoline distillate may be collected thereon. The tray 44 has a center vapor riser or down-pipe section 45 which extends above the bottom portion of the tray and permits the collection of the pool of distillate as well as an overflow of a portion of the stabilized distillate to the stripping section 43 which is in the lower end of the column 4, and wherein an absorber oil is formed for return to the upper portion of the column at the absorption section 40. The withdrawal of the stabilized gasoline fraction from the lower end of the stabilizing section 42, is made through line 46, a cooler 47, and line 48, having control valve 49. The cooler 47 may be of any conventional form and as indicated here may be of a heat exchange type suitable to cool the fraction as may be desired prior to its passage through line 48 to a suitable place of storage or to other treating equipment.

In the particular embodiment illustrated in Figure 2, there is shown a reboiler 50, connecting by means of line 51 and 52 to the pool of liquid on tray 44 such that controlled heating may be supplied to the distillate and insure the withdrawal of the desired fraction having desired vapor pressure characteristics. In a normal operation of the unit, a major portion of the stabilized fraction is withdrawn from column 4' through lines 46 and 48, with only a minor portion of the stabilized distillate being passed downwardly into the lower end of the column to undergo stripping within the lower stripping section 43. The lower stripping section 43 is operated to supply a continuous stream of absorption oil for the upper portion of the column. The valve 49 in the gasoline withdrawal line 48 is preferably controlled automatically by a level controller Within the stripping section so as to automatically control the amount of overflow through the downpipe 45 and maintain a constant level of liquid within the lower end of the column.

Another reboiler 53 connects with the liquid in the lower end of the column 4 through line 54 having valve 55 and'a return line 56, such that sufiicient heat may be supplied to the liquid fraction to effect heating and a substantial removal of all the light ends in the lower boiling vapors from the residual distillate and provide thereby a resulting absorption oil stream which is sufficiently lean to effect an efficient absorption of light ends and gases within the upper absorption section 40. The lean absorption oil which is formed in the lower stripping section 43, is withdrawn through line 57 having control valve 58 and passed through a cooler 5'9, such that a partially cooled absorption medium is passed through line 60 to the pump 61, which in turn discharges Into the line 41 connecting with the top of the column 4' at the upper portion of the absorption section 40. Although not shown in the drawing, suitable automatic controlling instruments may be utilized to regulate the rate of fiow of the absorption oil' stream to the top of the column, such as the use of an automatic flow controller in line 41 to control valve 58 or to regulate the speed of the pump 61.

In the particular embodiment of the apparatus shown, independent heating is provided in the stabilizing stripping sections by the reboilers 50 and 53. The separate heating in each of the sections is desirable to permit the independent control and regulation of the heat supplied to the stripping section to provide a desired lean oil for absorbing purposes without unduly affecting the characteristics of the distillate being withdrawn from the stabilizing section 42. In other words, the reboiler 56) can be operated to provide the desired vapor pressure characteristics of the gasoline fraction being withdrawn through line 46 and compensate for variations in the vapors and gases being passed upwardly to that section from the lower shipping section 43. It is, however, not intended to limit the present invention and the improved operation for removing the side-cut streams from a combined column of this type to a unit utilizing independent heating and two reboilers in the lower portion of the column. By proper regulation and control of the lower portion of the column, a single reboiler, such as located in the position of the reboiler 53 and connecting with the lower stripping section, may be used to provide the heat for effecting stabilization and fractionation within the intermediate section 42, as well as for stripping the residual distillate in the lower section of the column to provide a lean absorption oil. In such an operation, a single reboiler may be controlled to supply heat in response to minor variations in the temperature at the point of withdrawal of the stabilized distillate from the intermediate stabilizing section. However, the use of a single reboiler in the combined column does not provide a desired flexibility in operation, whereby the absorption oil characteristics and the vapor pressure of the gasoline fraction being withdrawn from the column can each independently be controlled to a close point and not surging caused within the entire combined column.

It is not intended to limit the invention to the recovery of fractions from a charge stream obtained from any one conversion operation. For example, the mixture may well comprise the product stream from a thermal or catalytic cracking unit, or from a catalytic reforming operation, which in turn may be effected through the use of any one of a number of various reforming catalysts. The invention is also not to be limited to the recovery of components from a mixture of normally liquid and normally gaseous components since it is equally adaptable to the recovery of components from a normally liquid mixture such as gasoline and/or gasoline fractions. The charge thus is a mixture that may be separated into a liquid fraction and a gaseous fraction in a separator of a flash drum type. The mixture may also be characterized as a mixture of light components and heavy components, differing in boiling point, that is lower boiling components and higher boiling components. In one embodiment the invention is directed to the recovery of a desired component from a mixture containing hydrocarbons boiling within the gasoline range. The operation of the present fractionating and stabilizing system is not limited to any particular operating pressure, it may be at a substantially atmospheric pressure or several hundred pounds per square inch, depending primarily upon the conversion operation and the pressure at which it is carried out.

The improved operation of the present invention has another particular advantage or useful feature when used in connection with certain catalytic reforming oper-.

ations, such as where it is desired to remove much of the light normally gaseous hydrocarbon fractions from the overhead gas stream in order that an enhanced concentration of hydrogen may be effected, to aid in its recovery for reuse in the conversion step. In other words, the improved operation may be carried out to provide primarily hydrogen within the overhead gas stream so that the hydrogen may be subsequently recovered and returned to the reforming section for reuse therein. In carrying out such an operation, the operating conditions affecting the absorption of the lower boiling normally gaseous hydorcarbon constituents in the gas are regu lated so that the hydrocarbon fractions are carried to the fractionation portion of the rectification section whereby they may be removed as vaporous side-cuts with out condensing them at the column, and permitting the resulting overhead gas stream to be primarily hydrogen with only minor quantities of the lighter hydrocarbon gases and vapors.

I claim as my invention:

1. A method for fractionally separating and recovering a desired normally gaseous component from a mixture thereof with lower boiling components and higher boiling components in the gasoline boiling range comprising, separating said mixture into a gaseous fraction and a liquid fraction, each containing a portion of said desired component and said gaseous fraction containing a major proportion of components boiling below said desired component and said liquid fraction containing a major proportion of components boiling above said component, introducing the separated lower boiling fraction to a fractionating column at an intermediate point in the height of the column, simultaneously introducing the separated higher boiling fraction to said column at a lower point in the height thereof, contacting the gaseous fraction with a lean absorption oil in the upper portion of the column, passing the resultant enriched absorption oil downwardly in the column below said intermediate point and in this portion of the column removing dissolved gases from said liquid fraction and the absorption oil, withdrawing a liquid stream of said higher boiling components from the column below said lower point, further distilling a portion of said higher boiling components to obtain said absorption oil and introducing the latter to the upper portion of the column, discharging a gaseous stream of said lower boiling components from the upper portion of the column, removing from the column between said points an intermediate fraction consisting essentially of said desired component and recovering said intermediate fraction.

2. The method of claim 1 further characterized in that said intermediate fraction is removed in gaseous phase from the column between said points.

3. The method of claim 1 further characterized in that said desired component comprises propane.

4. The method of claim 1 further characterized in that said desired component is a propane-butane fraction.

5. A method for fractionally separating and recovering propane from a mixture thereof with hydrocarbons lower boiling and higher boiling than propane comprising, separating said mixture into a gaseous fraction and a liquid fraction, each containing a portion of said propane and said gaseous fraction containing a major proportion of components boiling below propane and said liquid fraction containing a major proportion of components boiling above propane, introducing the lower boiling fraction to a fractionating column at an intermediate point in the height of the column, simultaneously introducing the higher boiling fraction to said column at a lower point in the height thereof, contacting the gaseous fraction with a lean absorption oil in the upper portion of the column and absorbing propane in the oil in this part of the column, passing the resultant enriched absorption oil downwardly in the column below said intermediate point and in this portion of the column removing dissolved gases from said' liquid fraction and the absorption oil, withdrawing a liquid stream of said higher boiling hydrocarbons from the column below said lower point, further distilling a portion of said higher boiling components to obtain said absorption oil and introducing the latter to the upper portion of the column, discharging a gaseous stream of said lower boiling hydrocarbons from the upper portion of the column, and removing an intermediate fraction consisting essentially of propane from the column between said points.

6. The improved process for the segregation of hydrocarbons boiling in the motor fuel boiling range from a vaporous mixture containing said hydrocarbons, lower boiling hydrocarbons and predominantly large mol percent of hydrogen which comprises segregating a vaporous stream comprising said lower boiling hydrocarbons, some of said hydrocarbons boiling in the motor fuel boiling range and the hydrogen from a condensed hydrocarbon stream substantially completely free of hydrogen in an initial separation zone, passing said condensed stream to a stabilization zone wherein a separation is made between hydrocarbons boiling in the motor fuel boiling range and lower boiling hydrocarbons, passing a portion of said hydrocarbons boiling in the motor fuel boiling range to a distillation zone wherein a separation is made between low boiling hydrocarbons and high boiling hydrocarbons, passing at least a portion of said high boiling hydrocarbons from said distillation zone into the top of an absorption zone as an absorption oil, removing overhead from said stabilization zone lower boiling hydrocarbons, cooling the same and passing the cooled stream to a secondary separation zone, segregating uncondensed hydrocarbons and passing the same to a lower point of said absorption zone, passing said vaporous stream from said initial separation zone into an intermediate point of said absorption zone, countercurrently contacting the upflowing vaporous stream with said downflowing absorption oil, whereby said hydrocarbons boiling in the motor fuel boiling range are absorbed in said absorption oil, removing hydrogen and hydrocarbons boiling below the motor fuel boiling range overhead from said absorption zone and removing said absorption oil comprising said higher boiling hydrocarbons and absorbed hydrocarbons from the bottom of said absorption zone and passing the same to said stabilization zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,072,456 Keith Mar. 2, 1937 2,189,265 Keith Feb. 6, 1940 2,296,992 Gary Sept. 29, 1942 2,468,750 Gudenrath May 3, 1949 2,668,139 Baird et a1 Feb. 2, 1954 2,719,816 Rich Oct. 4, 1955 

1. A METHOD FOR FRACTIONALLY SEPARATING AND RECOVERING ING A DESIRED NORMALLY GASEOUS COMPONENT FROM A MIXTURE THEREOF WITH LOWER BOILING COMPONENTS AND HIGHER BOILING COMPONENTS IN THE GASOLINE BOILING RANGE COMPRISING, SEPARATING SAID MIXTURE INTO A GASEOUS FRACTION AND A LIQUID FRACTION, EACH CONTAINING A PORTION OF SAID DESIRED COMPONENT AND SAID GASEOUS FRACTION CONTAINING A MAJOR PROPORTION OF COMPONENTS BOILING BELOW SAID MAJOR PROPORTION OF COMPONENTS BOILING ABOVE SAID COMPONENT, INTRODUCING THE SEPARATED LOWER BOILING FRACTION TO A FRACTIONATING COLUMN AT AN INTERMEDIATE POINT IN THE HEIGHT OF THE COLUMN, SIMULTANEOUSLY INTRODUCING THE SEPARATED HIGHER BOILING FRACTION TO SAID COLUMN AT A LOWER POINT IN THE HEIGHT THEREOF, CONTACTING THE GASEOUS FRACTION WITH A LEAN ABSORPTION OIL IN THE UPPER PORTION OF THE COLUMN, PASSING THE RESULTANT ENRICHED ABSORPTION OIL DOWNWARDLY IN THE COLUMN BELOW SAID INTERMEDIATE POINT AND IN THIS PORTION OF THE COLUMN REMOVING DISSOLVED GASES FROM SAID LIQUID FRACTION AND THE ABSORPTION OIL, WITHDRAWING A LIQUID STREAM OF SAID HIGHER BOILING COMPONENTS FROM THE COLUMN BELOW SAID LOWER POINT, FURTHER DISTILLING A PORTION OF SAID HIGHER BOILING COMPONENTS TO OBTAIN SAID OBSORPTION OIL AND INTRODUCING THE LATTER TO THE UPPER PORTION OF THE COLUMN DISCHARGING A GASEOUS STREAM OF SAID LOWER BOILING COMPONENTS FROM THE UPPER PORTION OF THE COLUMN, REMOVING FROM THE COLUMN BETWEEN SAID POINTS AN INTERMEDIATE FRACTION CONSISTING ESSENTIALLY OF SAID DESIRED COMPONENT AND RECOVERING SAID INTERMEDIATE FRACTION. 